1. Field of the Invention
The present invention relates to a data compression apparatus and method, a recording medium, and a data expansion apparatus and method. In particular, the invention relates to a data compression apparatus and method, a recording medium, and a data expansion apparatus and method which compress consecutive data efficiently, i.e., at a high compression ratio, and store or expand compressed data.
2. Description of the Related Art
In storing a large amount of data such as graphics data on a recording medium such as an optical disc, it is a common procedure to compress the data and record compressed data. The compressed data are expanded in using the data.
For example, where data packets each consisting of data A to L occur consecutively as shown in FIG. 1, those data are sequentially compressed according to a predetermined compression scheme and compressed data are recorded on a recording medium or transferred via a predetermined transmission line.
However, in compressing, for instance, data (coordinate values, luminance values, etc.) corresponding to apices of polygons that are used in computer graphics, a sufficiently high compression ratio is not obtained if the run-length method is applied to the data themselves. Further, since data of this type is low in the degree of unevenness in a frequency profile, a sufficiently high compression ratio is not be obtained by a method that utilizes frequency-based classification such as DCT (discrete cosine transformation). Therefore, transfer or storage of data of this type requires high-speed transfer processing or a recording area of a large capacity, resulting in a difficulty in reducing the cost.
Where a low-speed transmission line or a recording area of a small capacity, the amount of data needs to be reduced by for instance, lowering image resolution, resulting in a difficulty in rendering graphic images with good image quality.